1. Field of the Invention
The invention relates generally to a measurement device and, more particularly, to a measuring device for inspecting and verifying weld profiles.
2. Background Description
Gas tungsten arc welding is used in many different applications to make welds for piping systems. For example, gas tungsten arc welding is used in clean rooms to make welds on pipelines that supply various fluids and gases to the equipment in the clean rooms. One such clean room is for the manufacturing of semiconductor chips and other similar components.
At the present time, many proposed standards are being devised in order to ensure that gas tungsten arc welding meets certain minimum requirements in the clean room and semiconductor environment. These standards will ensure that semiconductor manufacturing applications, for example, operate at peak efficiency. In particular, SEMI™ GTA (gas tungsten arc) task force is currently devising weld standards and tolerances for the gas tungsten arc welds used in semiconductor manufacturing applications. More specifically, SEMI is setting standards for maximum and minimum weld bead convexity, concavity, and width, and maximum and minimum offset from perfect axial alignment of successive pipes in the pipeline.
It is currently theorized that if a weld does not conform to certain tolerances, gas flow over the weld bead will be disturbed potentially resulting in a Venturi effect. The Venturi effect results in a pressure differential over the weld, which, in turn, causes a moisture buildup at the weld bead. This moisture buildup will cause corrosion in the pipe thus introducing impurities into the system. These impurities will reduce semiconductor yield thus causing a reduced manufacturing yield, as well as affecting the integrity of the weld. The same problems occur when successive pipes along the pipeline are axially misaligned. Thus, it is imperative that all welds are within certain strict tolerances so as to minimize yield loss due to misalignment of pipes as well as improper weld beads.
To ensure that the weld bead is within certain tolerances, the welder will make periodic sample welds, or coupons, on the pipeline. A longitudinal cross section of the pipeline will then be cut in order for the welder to measure the weld parameters. That is, the welder will inspect the coupons for penetration, bead concavity, bead variation, oxidation and other variables. These coupons and observations, along with the known diameter and other dimensions of the tungsten tip and pipe, itself, are then used to calibrate the welding machine. Thereafter, the welder can begin the welding process using the calibrated welding machine.
However, in order to measure the weld parameters the welder must use complex and cumbersome devices, even using complex mathematical formulas based on the diameter and wall thickness of the pipe. For example, U.S. Pat. No. 2,603,872 to Jones teaches a gauge for measuring curvature, and a standard micrometer can be used to measure the width of the weld bead. However, these devices are mechanically cumbersome and require complex calculations or manipulations to arrive at a meaningful result. Furthermore, the actual numerical measurement of the weld bead is not as important to the welder as being within certain weld tolerances based on many variables including, for example, the different multipliers multiplied by the pipe wall thickness. Thus, the prior art devices tend to provide irrelevant data to the welder.
Additionally, existing devices are capable of inspecting and verifying only one aspect of the weld bead at a time, thereby requiring the welder to carry multiple cumbersome devices. Consequently, the welder cannot employ existing devices simply and rapidly. Similar problems exist with respect to devices for use in verifying axial alignment of pipes, such as the device shown in U.S. Pat. No. 4,255,860 to Ragettli.